MONTREAL — A chunk of concrete fell from an overpass in the West Island onto the hood of a vehicle on Highway 40 Monday, but government officials said the structure isn’t falling apart.

Transport Quebec confirmed late Monday that a section of concrete beneath the guard rail of the overpass came loose on Monday morning and fell into the oncoming traffic below. No one was injured in the incident, though photos from the scene show a BMW SUV by the side of the road with a badly damaged hood.

“We’re removing whatever loose concrete remains along the guard rail, but none of the damage is structural,” said Transport Quebec spokesperson Sarah Bensadoun. “The damage is entirely esthetic, our latest inspection reports show that the overpass is in good shape and was only scheduled for minor repairs in three to five years.”

The incident was reported around 11:37 a.m. at the Hymus and Henri-Bourassa Blvd. viaduct. It forced the transport ministry to shut down traffic on the overpass and Highway 40 westbound so that government engineers could determine exactly what caused the concrete to come tumbling down.

Transport Quebec reopened the highway around 2:30 p.m. but traffic remained snarled until the end of rush hour. The overpass itself remained closed as of Monday afternoon.

Though initially, Transport Quebec was hesitant to confirm the falling debris came from the overpass, there were signs of superficial damage across the structure.

Portions of the overpass are badly eroded and rusted rebar is exposed along much of its bottom edge. Engineers from the transport ministry were slated to return to the site of the accident late Monday to conduct a more thorough inspection. That will result in the complete closure of Highway 40 in both directions for several hours overnight.

It’s possible the recent wave of freezing temperatures followed by unseasonably warm weather could have contributed to the incident, according to McGill University engineering professor Saeed Mirza.

“If there are already cracks in the structure, moisture will seep into it,” Mirza told The Gazette. “As the moisture freezes, it expands and tries to pry the concrete apart. If it keeps freezing and thawing, it’s only a matter of time before the concrete falls off.”

Bensadoun said the recent erratic weather patterns may have put undue pressure on the overpass. Like most of Montreal’s crucial infrastructure, the viaduct was built during the 1960s construction boom that swept through Montreal and it is beginning to show its age.

“During the lead up to Expo 67 (when Montreal hosted the World’s Fair), a lot of our infrastructure was built in a hurry,” Mirza said. “We’ve been seeing lots of evidence of that lately with damage on the Champlain Bridge, the Turcot Interchange and overpasses everywhere.”

Mirza said one strategy to help prevent moisture from eroding infrastructure is with a method called air entrainment.

“What happens is we deliberately introduce air bubbles into the concrete so that if there’s any moisture, it will expand into a space that’s already provided for it,” Mirza said. “Basically, it’s a common practice now and it’s simply a matter of designing our structures better.”